Its a good idea.
Twin 70mm throttle bodies give the equivalent surface area to a single 100mm throttle body.
The cheapest way to do it would be to cut the plenum in half down the middle, and then weld two halves together. Then just drill a new hole for the ISCV and CSI, and weld up the half ISCV hole that would now be at the rear.
Cosmetically this won't look the best, which is why I didnt do it this way. But it would be the easiest IMO.
Either that or just weld the snout and flange onto the side of the plenum, and use dual throttle cables.
FYI, the snout on mine is upright, but the flange and TB are upsidedown.
This give a nice balance between cosmetics, and the ease of throttle linkage.